Dual Band Infrared (DBIR) Imaging has numerous advantages over conventional thermal imaging which utilizes only a single band. Conventional thermal imaging is difficult to interpret. It yields imprecise information that is insensitive to the subtle heat flow anomalies produced by subsurface flaws. These conventional imaging techniques fail to distinguish between surface emissivity clutter and true temperatures. In addition, emissivity-related noise, typically 1.degree. C. or 2.degree. C., cannot be removed using a single passive thermal IR band even when used in conjunction with another active laser reflectance IR band.
DBIR imaging has most recently been applied to the detection of buried land mines by exploiting temperature differences between the mine site and the surrounding soil. U.S. Pat. No. 4,005,289 describes this method, its contents which are incorporated herein by reference.
Lap joints were studied in the present invention, because a lap joint that had the adhesion bond removed (disbond) played a significant role in causing damage to the Aloha Aircraft fuselage on the aged Boeing 737 jetliner which produced loss of life several years ago.